A pump for a primary nuclear reactor cooling material is provided with a rotating shaft that rotates about an axis which extends in a vertical direction and a housing that surrounds the rotating shaft. A plurality of stages of shaft seals, which are arranged apart from each other in the vertical direction, are provided in a space between the rotating shaft and the housing. The plurality of stages of shaft seals perform pressure reduction so that high-pressure pressurized water on a lower side has the atmospheric pressure on an upper side (for example, refer to PTL 1).